Laser processing may be conducted on numerous different types of workpieces using various lasers to effect a variety of processes. Lasers may be used to form, for example, a hole and/or blind via in a single layer or multilayer workpiece. Semiconductor wafer processing may include various types of laser micromachining including, for example, scribing, dicing, drilling, removal of semiconductor links (fuses), thermal annealing, and/or trimming passive thick or thin film components.
Conventional laser drilling or scribing techniques include, for example, using CO2 lasers with wavelengths in the far-infrared range. However, such lasers may generally require high energies to ablate some integrated circuit (IC) processing materials.
Further, such processing techniques generally use long pulses with slow rise and fall timing in the pulse being as much as approximately 50 μs. Accordingly, the long pulses may allow excessive heat diffusion that causes heat affected zones, recast oxide layers, excessive debris, chipping and cracking. Further, pulsed CO2 lasers generally tend to have a high magnitude of pulse-to-pulse energy instability that may negatively impact the consistency of processing quality.
Conventional CO2 drilling or scribing systems generally use radio frequency (RF) pulsed CO2 lasers with typical relaxation times of the excited state that are between approximately 50 μs and approximately 100 μs. To produce discrete laser pulses, a generally acceptable pulse repetition frequency (PRF) is approximately the inverse of twice the relaxation time. Thus, CO2 lasers typically provide a maximum PRF between approximately 5 kHz and approximately 10 kHz. When an increased throughput is desired, these low PRF values may reduce processing quality. For example, when a scribing system increases the speed at which it moves a laser beam with respect to a workpiece, structures along the kerf due to the separation between pulses become prominent at low PRFs. Such structures in the kerf reduce processing quality.